International application WO 01/72572 describes a wheel support device that allows for a degree of camber freedom of the wheel relative to the suspension elements. This degree of freedom is controlled either in an active way, for example by a jack as a function of rolling parameters of the vehicle, or passively by the forces exerted on the wheel in the contact area.
European patent application EP 1247663 also concerns such systems and proposes to guide the camber movement of the wheel by using an element which pivots around a substantially vertical axis articulated between the wheel carrier and the suspension elements.
European patent application EP 1275534 also concerns such systems and proposes the use of a curved slide-bar to guide the camber movement of the wheel carrier relative to the suspension elements.
One of the difficulties encountered in the design of these systems stems from the fact that large forces have to be transmitted from the road to the body (and vice-versa) via the ground contact system and in particular the tyre, the wheel carrier and the suspension. These forces produce large mechanical stresses with all the consequences that result from these for the guiding precision of the wheel and for the reliability of the systems. Viewed from the body of the vehicle, the forces transmitted by the road are generally divided as follows: a transverse force (horizontal and perpendicular to the wheel plane), a longitudinal force (horizontal and parallel to the wheel plane), a vertical force, a torque called the “spin” torque (around the axis of the wheel), a torque called the “overturning” torque (around the longitudinal axis) and a “self-alignment” torque (around the vertical axis). In addition to these forces transmitted by the road, the wheel transmits to the body forces stemming from the inertia forces it undergoes, in particular the centrifugal force which acts around curves.
In the support and suspension systems described in the patent applications mentioned earlier, by comparison with conventional suspension systems a degree of freedom has been provided so as to allow some wheel camber relative to the body. This additional mobility can be provided in several different ways but common to them all is the fact that increasing the number of components and articulations or pivots tends to decrease the rigidity and/or robustness of the system as a whole. Moreover, it is difficult to compensate this rigidity deficit by enlarging the sections of the various elements because the space available is generally limited. In effect, such variable-camber suspensions should preferably not interfere with the compromises established in the context of space occupied (the term “packaging” is also used).
A problem of these systems is therefore their less than perfect rigidity, in particular in relation to the longitudinal force, the self-alignment torque and the rolling torque.
In the application WO 01/72572 it is proposed, for passive systems, that the instantaneous centre of rotation for the camber movement of the wheel relative to the suspension elements should be located below ground level so that the transverse forces acting in the contact area generate a torque which tends to tilt the wheel plane in the direction desired (this instantaneous centre of rotation is called the “first instantaneous centre of rotation” in the document WO 01/72572). However, although under this condition the transverse forces generate a torque along the camber axis which tends to tilt the wheel in the direction desired, the efficacy in terms of camber variation is very different depending on the configurations used. Yet in practice, the sensitivity of the camber to forces in the contact area is an important criterion. In effect, it is generally sought to design a wheel support and suspension system such that the passive camber variation is predictable, stable and satisfactory in terms of maximum inclination. This is particularly important for high-performance vehicles. For such vehicles the search for optimum performance includes optimisation of the longitudinal and transverse grip. This optimisation is only possible if the camber angle of the wheel is at all times ideal for the operation of the tyre. An ideal camber from the standpoint of tyre grip is a camber that allows optimisation of the pressure distribution in the contact area, i.e. one which, for example, allows compensation of the effect on the pressure distribution in the contact area that results from lateral deformations of the tyre when it is slipping (typically, while rounding a bend).